(1) Field of the Invention:
This invention relates to plastic lenses, especially, to plastic lenses made of a brominated aromatic copolymer which has a high refractive index and is high in dyeability.
(2) Description of the Related Art:
Both spectacle lenses and contact lenses are generally used for the correction of vision. As spectacle lenses out of these lenses, plastic lenses made of a synthetic resin have found wide-spread utility for their useful advantages such as lightweights, easy machinability, stability and dyeability in addition to inorganic glass lenses.
A variety of characteristics are required for such plastic lenses. Among these, it is essential that the refractive index is high and the light dispersiveness is low. Namely, it is extremely preferred for a lens to have a high refractive index, since the high refractive index facilitates the designing of the lens to impart desired characteristics, and the so-called peripheral thickness of the lens can be reduced substantially and its weight reduction can also be achieved at the same time.
It is one advantage of plastic lenses over inorganic glass lenses that the plastic lenses have high dyeability, whereby optical characteristics suitable for various applications can be imparted to the plastic lenses. In spectacle lenses for example, the correction of vision is most important as their function. There is however recent tendency that spectacle lenses themselves are taken as a sort of fashion-related elements. The commercial value of spectacle lenses is declining so long as their function of visual correction is concerned merely. It has started taking the color tone and the like of lenses as important in order to make the lenses match a frame to be used. In order to meet this move, it is becoming important to apply dyeing to spectacle lenses so as to dye them in various colors. This is a major cause for the starting of use of plastic lenses in place of inorganic glass lenses. It is an indispensable property for plastic lenses to have dyeability when their practical utility is taken into consideration.
It is diethylene glycol bis(ally carbonate) (hereinafter called "CR-39") that is used most widely as a material for spectacle plastic lenses these days. The refractive index of this CR-39 is however as low as 1.50 (n.sub.D =1.50).
For the reasons mentioned above, a great deal of work is now under way on polymers or copolymers which may provide plastic lenses having a high refractive index. Some of such polymers or copolymers have already been used actually.
For example, dimethacrylate and diacrylate copolymers in which a nucleus halogen-substituted aromatic ring is bonded to a methacryloxy or acryloxy group via an alkylene glycol group are proposed in Japanese Patent Publication No. 14449/1983. Further, polymers of a urethanated (meth)acrylic monomer obtained by reacting a brominated aromatic monomer, which contains a hydroxyl group, with a polyfunctional isocyanate are proposed in Japanese Patent Laid-Open No. 51706/1985.
The polymers proposed in the above patent publications are satisfactory as far as their refractive indexes are concerned. They are however accompanied by a drawback that their dyeability is too low to dye them in practice. They therefore involves a problem that a substantial limitation is imposed on their application field upon providing them for actual applications.